The present invention is directed to a spray head for use with a can or container containing a liquid exposed to the pressure of a propellant.
Spray heads of the type for so-called aerosol cans or containers are known, for instance, from WO No. 86/04163. However, the known design is extremely complex. It comprises a plunger supported in the spray head for longitudinal movement and biased by a helical compression spring so that, when the aerosol can is not in use, the fluid communication with the spray can is closed. At its one side, the plunger is exposed to ambient pressure while the other side is exposed to the overpressure in the can when the dispensing valve thereof has been opened. Then, the plunger is moved under the action of the overpressure in the can against the action of the resilient biasing force and the action of ambient pressure to a fluid-communication release position while at the same time a constriction of the flow cross-section and a corresponding restriction of the dispensed fluid is provided. The plunger which is movably supported within the spray head is sealed relative to a corresponding cylinder wall by means of two sealing rings of rubber or like material disposed at either end of the plunger. The sealing rings will contact the medium to be sprayed, said medium in most cases reacting rather aggressively so that the sealing rings swell up and the plunger movement becomes heavy until finally the plunger fails, which happens especially after a prolonged period of non-use. In the last-mentioned case there even is the risk of the plunger becoming unable to be moved to an open position due to an excessive "breakaway force", and consequently the spray nozzle remains closed and the aerosol can must be discarded although still partly filed. The waste rate on the consumer's side caused thereby is unacceptable.
It is known from US-PS No. 4,487,334 to provide a variable throttle means upstream of the dispensing valve in the can interior, said throttle means controlling the flow cross-section of the fluid passage leading to the dispensing valve in dependence on the propellant pressure. This design is likewise extremely complex and also rather unreliable in respect of continued proper operation due to unavoidable leakages in the area of the throttle.